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java.lang.UnsupportedClassVersionError

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java.lang.UnsupportedClassVersionError

I compiled a few java classes with Eclipse and uploaded on Google App Engine. It didn’t work.

In the logs, it shows:

java.lang.UnsupportedClassVersionError …. minor 51

I googled on the Internet. Someone said:

It means that you compiled your classes under a specific JDK, but then try to run them under older version of JDK.

It spent me quite a lot of time to fix it.

Google App Engine said it supported Java 5 or 6, in other words, jdk1.5.0 or jdk1.6.0.

I added java path to the .ini file. Nothing changed. I think, this step is useless.

On Eclipse, on Windows->Preference. Click “compiler” to open the window, change JDK to 1.6. And JRE’s directory pointed to the JRE6.

It didn’t work. Later on, I found on the windown above, there is a link to remind me to change the JDK of my Application. I did it. Then it works.:))

An example code for using DataStore on Google App Engine

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java file

import java.util.Date;
import com.google.appengine.api.datastore.DatastoreService;
import com.google.appengine.api.datastore.DatastoreServiceFactory;
import com.google.appengine.api.datastore.Entity;
import com.google.appengine.api.datastore.KeyFactory;
import com.google.appengine.api.datastore.Key;
import com.google.appengine.api.datastore.EntityNotFoundException;
import java.io.IOException;

public class DataStore {

    DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
    Date putDate = new Date();
    Entity entity = null;
    String links = “”;

    public String createEntity(String headlines, String entity_key) {

        entity = new Entity(headlines, entity_key);

        entity.setProperty(“Name”, null);
        entity.setProperty(“Link”, null);
        entity.setProperty(“Date”, putDate);
        entity.setProperty(“Description”, null);
        datastore.put(entity);

        return “create”;
    }

    public String updateEntity(Key entity_key, String name, String link, String description) {

        try {
            entity = datastore.get(entity_key);

            entity.setProperty(“Name”, name);
            entity.setProperty(“Link”, link);
            entity.setProperty(“Date”, putDate);
            entity.setProperty(“Description”, description);

            datastore.put(entity);

        } catch (EntityNotFoundException e) {
        }

        return “update”;
    }

    public String deleteEntity(Key entity_key) {

        datastore.delete(entity_key);
        return “delete”;
    }

    public String getPropertiesOfEntity(Key entity_key) {

        try {

            entity = datastore.get(entity_key);
            String media_name = (String) entity.getProperty(“Name”);
            String news_links = (String) entity.getProperty(“Link”);

            links = media_name + news_links;

        } catch (EntityNotFoundException e) {
        }

        return “get” + links;
    }

    public String getLinks() {

        String key_str = “H”;

        Key entity_key = KeyFactory.createKey(“Headlines”, key_str);

        //       createEntity(“Headlines”, key_str);
        //       updateEntity(entity_key, “1”, “2”, “3”);
        //     deleteEntity(entity_key);

        return “Well done” + getPropertiesOfEntity(entity_key);
    }
}

 

jsp file：

<%@page contentType=”text/html” pageEncoding=”UTF-8″%>
<%@ page import=”DataStore” %>
<!DOCTYPE html>
<html>
    <head>
        <meta http-equiv=”Content-Type” content=”text/html; charset=UTF-8″>
        <title>JSP Page</title>
    </head>
    <body>
        <h1>Hello World!</h1>

        <%

            DataStore Database = new DataStore();

        %>

        <%= Database.getLinks() %>

    </body>
</html>